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Date:   Fri, 30 Oct 2020 16:00:04 +0000
From:   Mark Rutland <mark.rutland@arm.com>
To:     Jann Horn <jannh@google.com>
Cc:     Marco Elver <elver@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christoph Lameter <cl@linux.com>,
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Subject: Re: [PATCH v6 3/9] arm64, kfence: enable KFENCE for ARM64
Message-ID: <20201030160004.GE50718@C02TD0UTHF1T.local>
References: <20201029131649.182037-1-elver@google.com>
 <20201029131649.182037-4-elver@google.com>
 <CAG48ez11T4gXHkhgnM7eWc1EJQ5u7NQup4ADy75c1uUVPeWGSg@mail.gmail.com>
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On Fri, Oct 30, 2020 at 03:49:26AM +0100, Jann Horn wrote:
> On Thu, Oct 29, 2020 at 2:17 PM Marco Elver <elver@google.com> wrote:
> > @@ -312,6 +313,9 @@ static void __do_kernel_fault(unsigned long addr, unsigned int esr,
> >             "Ignoring spurious kernel translation fault at virtual address %016lx\n", addr))
> >                 return;
> >
> > +       if (kfence_handle_page_fault(addr))
> > +               return;
> 
> As in the X86 case, we may want to ensure that this doesn't run for
> permission faults, only for non-present pages. Maybe move this down
> into the third branch of the "if" block below (neither permission
> fault nor NULL deref)?

I think that'd make sense. Those cases *should* be mutually exclusive,
but it'd be more robust to do the KFENCE checks in that last block so
that if something goes wrong wrong within KFENCE we can't get stuck in a
loop failing to service an instruction abort or similar.

Either that, or factor out an is_el1_translation_fault() and only do the
KFENCE check and is_spurious_el1_translation_fault() check under that.

Thanks,
Mark.